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The case for diet soda: It gets a bad rap, but the research tells a different story

(Wilfredo Lee/AP)

The nutrition community doesn’t like diet soda. Of all the groups that make dietary recommendations, I can’t find one that lends full-throated support. “Limit low-calorie sodas,” says the American Heart Association, and “stick to water.” The Center for Science in the Public Interest says it’s “best to avoid” artificial sweeteners. The Canadian dietary guidelines discourage them. The U.S. dietary guidelines are decidedly meh. Although added sugar is a top public health concern, diet soda is consistently met with something between distrust and hostility.

Dig into the research, though, and you don’t find a lot of substance. The hostility-to-evidence ratio is way out of whack. What gives?

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I’ll try to answer that, but we have to begin with what is arguably the most important thing to know about low-calorie sweeteners: You consume them in teeny tiny quantities. Take sucralose, the ingredient in Splenda. The Food and Drug Administration has determined that the Acceptable Daily Intake (which it derives by determining the safe level and dividing by 100) is 5 milligrams per kilogram of body weight. If you weigh 150 pounds, that means you can eat 340 milligrams, the amount in 28 packets of Splenda, every day.

The important number there is 340 milligrams — about a third of a gram. If it were sugar, that would be one-third of a quarter-teaspoon.

That doesn’t mean it’s harmless. “There are things where tiny amounts will kill you,” says Alice H. Lichtenstein, professor of nutrition science and policy at Tufts University’s Friedman School of Public Health and co-author of the American Heart Association’s position on low-calorie sweeteners, “but we figure it out pretty quickly.”

Of course, things can hurt you without killing you, and we certainly can’t rule out harm from chronic, low-dose exposure. But one of the things that makes that less likely is the fact that we eat a mix of low-calorie sweeteners (LCSs) with different risks. “Chemically, they’re totally different,” Lichtenstein says, but when we talk about them, “the whole class of compounds get lumped together.”

The bad rap started with studies in the 1970s linking saccharin to bladder cancer. But it turned out that the mechanism wasn’t relevant to humans, and subsequent studies cleared it. But there are also concerns about what happens when your body experiences the disconnect between tasting something sweet but not taking in calories. The recent literature is filled with laundry lists of hazards that look like this one , from Stanford professor of medicine Christopher Gardner, and also a co-author of the American Heart Association position: “fostering a taste preference for sweet foods and beverages, making naturally sweetened foods less appealing, adversely altering feelings of hunger and fullness, reducing awareness of calorie intake, adversely altering gut microbiota, increasing glucose intolerance, substituting for healthier beverages, contributing to the perception that individuals can consume more calories from other foods, and contributing to the possible intake of other ingredients in LCS beverages that could be of concern such as caffeine and artificial colors.”

Yikes! I asked him about those dangers, and the first thing he said was “none of them are proven.” Then he added, “it’s all plausible.” When I told him my read is that the evidence was practically nonexistent, he nodded vigorously.

Gardner was particularly dismissive of the idea that tiny quantities of anything could mess with your gut microbiome. “We pummel people with fiber to try and move the microbiome, with limited success,” he said. It’s not easy, and the research on probiotics, which are intended to change your gut bacteria, indicates that it’s hard to do even when you’re trying. Nevertheless, the gut microbiome has become the conspiracy theory of nutrition: It’s where people go to prove something’s dangerous when there’s really no evidence that it is.

In fact, although gut bacteria is probably the most frequent issue I hear about, I could find exactly one study about it on humans, and that was an afterthought tacked on a mouse study. In it, seven people were fed saccharin for a week. Four of them had “poorer glycemic responses.” The rest of the research was on mice. Or sometimes rats. And if you take a bunch of mice that are genetically very similar, make sure they have no gut bacteria to begin with, and feed them different things, you will see different results because there is no noise to compete with what might be a very, very small signal. In human guts, it’s chaos, and changes have to be very powerful to be meaningful.

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Nevertheless, Gardner is in favor of LCSs “only as a gateway drug to water.” But if there’s some evidence that they can help at least a little with weight loss, and evidence for harm is practically nonexistent, why oppose them? “Because they’re only in crap.”

In a nutshell, this explains the hostility. Low-calorie sweeteners represent just about everything that’s wrong with our diet. They’re mostly synthetic. They play to the human preference for sweetness, which manufacturers leverage to sell us more, and then more again. A good chunk of the research is industry-sponsored. And they’re mostly in highly processed foods — or, as Gardner puts it, “crap.”

That’s what we’re not supposed to eat. We’re supposed to eat food, not too much, mostly plants. We’re supposed to turn it into home-cooked meals, with which we drink water. I’m on board! I’m squarely in the processed-food-causes-obesity camp. But given how far Americans are from these goals, should we let perfect be the enemy of perfectly okay?

People don’t want to drink water. They want to drink soda. But the attitude in the nutrition community isn’t just that you shouldn’t drink soda — regular or diet — it’s that you shouldn’t even want to drink soda. It’s puritanical, holier-than-thou and breathtakingly condescending.

Take the most recent meta-analysis, published in the British Medical Journal. “There was no compelling evidence” for benefits, the article concludes, but “potential harms . . . could not be excluded.” Why not the other way around? If there’s no compelling evidence for harms, and benefits can’t be excluded, pass the diet root beer.

“It’s like caffeine,” Lichtenstein says. “Everyone wants to find something wrong with it.” If you do, click on over to PubMed, the repository of scientific journals, and look. Check the research on humans. Ignore anything industry-sponsored. You’ll find plenty of lists of potential harms, but once you weed out speculation and focus on evidence, you don’t find scary.

But you know what is scary? Our obesity epidemic and the contribution from soda. Those sugar calories seem particularly insidious, since they go down easy and don’t make us feel full.

It’s not a no-brainer. Sugar consumption has been dropping since 1999, while obesity has just kept going up. When we look at population research on LCS users, they tend to weigh more and have generally worse health outcomes, so this is no panacea. (The fact that responsible authorities have been discouraging LCS use could also mean that people who are generally health-minded, and have good habits, don’t use them.) But when we look at clinical trials, people tend to consume fewer calories overall when they’re given an LCS instead of sugar, and over time they lose some weight. Not much, but name another obesity intervention that’s even moderately successful. If the nutrition community embraced low-calorie sweeteners, encouraged people who want to lose weight to make the switch, and cautioned against compensating with, say, Chunky Monkey, it’s hard to see the downside.

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There’s evidence for upside in the National Weight Control Registry, which tracks people who have lost at least 30 pounds and kept them off for at least a year. Only 10 percent of them report drinking sugar-sweetened drinks “regularly,” while 53 percent drink diet. Compare that to the population at large, 61 percent of whom report drinking a sugar-sweetened beverage on any given day, while only 15 percent report drinking a diet version. Low-calorie sweeteners clearly help at least some people.

I’m undoubtedly biased because I’m one of them. I never drink full-sugar soda, and I use sucralose in my smoothies and oatmeal. I’ve been overweight, and if I’m not constantly vigilant, the number on the scale starts to drift back up. Weight loss is hard, and I know I’m not the only one who needs all the help she can get.

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